This invention relates to an electric motor, and more particularly to a synchronous motor disposed in a real taking-up mechanism for a magnetic recording and reproducing apparatus.
A conventional reel taking-up mechanism includes a reel disk rotatable about the longitudinal axis thereof and including an upper end arranged to engage a take-up or a supply reel for a magnetic tape, and a rotor disk formed, for example, of soft iron and sandwiched between the lower surface of the disk and a circularly annular magnet concentric with the rotor disk to form a rotor of an electric motor. The annular magnet is magnetized so that four N poles alternate with four S poles to form an angular interval of 45 degrees between each pair of adjacent poles. Disposed below the annular magnet are a plurality of flatwise coils at predetermined equal angular intervals on a stator disk formed, for example, of soft iron and located coaxially with the motor disk to form a stator of the electric motor.
In operation a rotary magnetic field is established by the flatwise coils and rotates the annular magnet in synchronization with the rotary field, thus resulting in the rotation of the reel disk.
In conventional reel taking-up mechanisms such as described above, an eddy current is generated on the stator disk due to the rotation of the magnetized magnet, thus resulting in the disadvantages that a loss is caused in the resulting torque and the consumption of electric power is increased. Also there is a problem that the torque is not sufficient for each of the operations of fast forward feed and rewinding of an associated magnetic tape.
Accordingly it is an object of the present invention to provide a new and improved electric motor utilizing effectively an eddy current caused thereon to produce a torque to decrease the loss of a torque and therefore to reduce the consumption of electric power.
It is another object of the present invention to provide a new compact electric motor, including a pair of output shafts, which is capable of stabilizing the driving characteristic of an associated reel shaft and is capable of varying optionally a torque for driving the reel shaft.